Among the various iOS 5 features Apple chief Steve Jobs unveiled today at the company's Worldwide Developers Conference (WWDC) was iMessage, a messaging option for iOS devices reminiscent of RIM's BlackBerry Messenger.

Apple said iMessage "brings the functionality of iPhone messaging to all of your iOS devices―iPhone, iPad and iPod touch." It is built into the Messages app, and allows users to send messages, photos, videos, or contact information to other iOS 5 users via Wi-Fi or 3G.

Like BBM, however, iMessage will include delivery and read receipts, and typing indication, so you know if the person has received your message and if they are typing back. Apple's iMessage will also have secure end-to-end encryption.

In a statement, RIM didn't specifically mention iMessage, but talked up the success of BBM, as well as the keyboards and long-lasting battery life on Blackberrys, things the iPhone lacks.

"In addition to designing the industry's best keyboards, RIM's BlackBerry products and services are known for their data efficiency, security and battery performance, and these benefits were all built into BBM from the ground up," said Alistair Mitchell, RIM's vice president of the BBM platform. "BBM is a proven service that has grown to become a robust social platform, offering group chats, video sharing, voice note sharing and more."

Going forward, RIM is working to allow customers to discover and share apps via BBM, "creating a new breed of more engaging social app experiences," Mitchell said.

RIM has been battling against iOS and Android in recent years for smartphone dominance. Last week, comScore found that the continued popularity of the iPhone and Android-based devices helped Apple and Google maintain their lead over RIM in the first three months of the year, with iPhones snapping up 26 percent of the U.S. market.

In March, there were reports that RIM was planning on porting BBM to both the Android OS and eventually the Apple iOS platform, but it has not yet made any announcements. At last year's DevCon, RIM announced the launch of the BlackBerry Messenger Social Platform, a means of connecting the company's BBM messenger application to other apps.